Whatever works for you. There’s no definitive answer either way, says registered dietician Megan Pentz-Kluyts, citing a 2011 study published in the International Journal of Sport Nutrition and Exercise Metabolism which found that fasting before performing moderate exercise did not improve fat metabolism – the researchers recommended eating a light meal before exercising.

A study published in the journal Appetite found a year later that it was no more effective to run for 60 minutes on a treadmill before eating breakfast, than after, to aid weight loss, but for every one of these studies there’s a handful of others that argue otherwise, says Pentz-Kluyts.

Although you could probably wake up and work out for 45 to 60 minutes without eating, you may start to feel dizzy or hungry, so it’s better to have some carbs beforehand – if only so that you can actually enjoy the workout.

Choose something as simple as a banana, a slice of toast with some peanut butter, a few handfuls of cereal or some raisins, depending on the extent of your workout. If you’re exercising very early in the morning and can’t eat, drink a carb-rich drink or sip on a low-fat fruit smoothie.